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Environment Magazine September/October 2008

 

November-December 2017

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Living on the Edge: Emerging Environmental Hazards on the Peri-Urban Fringe

Dangers of Urbanization and Environmental Change

In this current era of global-scale social and environmental change, many researchers, policymakers, and practitioners anticipate increasing danger. In a warmer global climate system, for example, local effects become difficult to predict, and this presents unprecedented challenges for people worldwide.1 In addition, population growth, industrialization, and unplanned urban expansion are concentrating the world's people like never before, and often in risky situations. Since 2009 we have become a predominantly urban society.2 This historic rural-to-urban shift presents a host of new challenges, not the least of which is the anticipation and management of environmental risks and hazards.3

For many years, environmental scientists have been urging us to expect surprise in coupled human–environment systems, especially urban systems.4 The vulnerability of these systems to dangerous surprise is largely determined by the geography of human residency, including where the world's people live and how they interact with their local environments. Peri-urban fringe areas, where cities today experience their highest rates of change, are important places to study environmental hazard emergence. These are often wildland–urban interface (WUI) zones, where interactions between humans and natural environments are most apparent (see sidebar). Many recent disasters could be reexamined and perhaps better understood by focusing on human–environment interactions in peri-urban areas (Table 1). If we could better understand these interactions, we might better anticipate and manage what currently seem like unpredictable dangers.

Table 1. Prominent Disasters Reconsidered as Issues of the Peri-Urban Fringe (PUF) or Wildland–Urban Interface (WUI)

Event (Location and Year)Major Human–Environment InteractionsPUF/WUI Challenges
Pesticide gas release (Bhopal, India, 1984)Globalized economic developmentSpatial coincidence of heavy industry and unplanned urbanization
Hurricane Katrina (New Orleans, LA, 2005)Flood control, navigation and coastal industrializationPreserving historic urban character and protecting coastal ecosystems amidst growth in heavy industry
Wildfire (southeastern Australia, 2009)Changes in housing affordability and lifestyle leading to urban–rural migrationUrban housing market reform and rural land-use policy to minimize risk
Indus River flooding (Pakistan, 2010)Flood control and irrigated agricultureOverreliance on structural engineering (and associated “levee effects”) in densely populated floodplains
Tsunami and nuclear disaster (Fukushima, Japan, 2011)Nuclear energy developmentReconciling nuclear energy generation with high population density and scarce coastal land
Hurricane/Superstorm Sandy (New York and New Jersey, 2012)Coastal land developmentLand speculation and coastal real-estate growth amid sea-level rise
Typhoon Haiyan (Philippines, 2013)Coastal land developmentSubstandard housing within reach of storm surge
Kathmandu Valley earthquakes (Nepal, 2015)Globalized economic development and tourismDevelopment and enforcement of building codes and zoning on unconsolidated substrates
Wildfire (Chile, 2017)Plantation forestry and other forest management activitiesReconciling forestry, fire management, and urban planning

 

In this article we present a case study of human–environment interactions as the source of new environmental hazards in a peri-urban area. The case of a growing city, an exotic plant invasion, and an impending wildfire threat illustrates how the interactions of coupled human–environment systems produce hazards. It shows how gaps in risk awareness and hazard perception put communities in harm's way. It shows how limited resources and political will, along with difficulties in multilateral collaboration, can exacerbate threats to cities and their surrounding ecosystems. However, it also shows how public awareness, coordinated grass-roots effort, and the important work of a few dedicated actors can mitigate threats considerably. We discuss the case in the context of urbanization and environmental change, and we conclude by identifying cross-cutting lessons for application in other contexts.

SIDEBAR

As cities are expanding worldwide, the dichotomy between urban and rural is breaking down. Scholars of geography, planning, and urban ecology have written at length in recent years about the urban–rural divide as not a single line but a transition through zones, or a gradient. As today's cities expand and change in form, so do the environmental dangers that emerge at the peri-urban fringe. Some of the world's most threatening hazards, such as earthquakes, floods, droughts, and wildfires, pose new risks in and around expanding urban areas.

Spatial conceptualizations of the peri-urban fringe. (A) Boundary models range from urban-versus-rural dichotomies with fixed, clearly delineated, legal boundaries to models with multiple zones and fluid divisions among them. Zones or categories are created to represent meaningful differences among groups. For example, property tax rates vary among zones based on precisely drawn, legally binding lines. Property values, on the other hand, ignore these boundaries, and instead vary based on less tangible factors like proximity to schools, services, and other local amenities. This type of variability is nevertheless real and important in determining the social and ecological character of different locales in or near a city. Boundary models have prevailed in fields such as urban geography, policy, and planning. (B) Gradient models conceptualize cities as nodes or centers of urban-ness, surrounded by differences of many kinds, both social and ecological. Gradient models have been particularly useful in fields such as landscape ecology and urban ecology as a means to explain ecological processes in built environments and the role of cities within larger ecosystems. Both models assume singular, stand-alone urban centers surrounded by relatively undeveloped land, rather than modern urban forms such as pluricentric conurbations or metropolises, even though the latter are becoming common in some parts of the world. The wildland–urban interface (WUI) could be identified at any boundary (A), or anywhere along the urban-to-rural gradient (B), depending on the elements, characteristics, or processes of interest.

Spatial conceptualizations of the peri-urban fringe. (A) Boundary models range from urban-versus-rural dichotomies with fixed, clearly delineated, legal boundaries to models with multiple zones and fluid divisions among them. Zones or categories are created to represent meaningful differences among groups. For example, property tax rates vary among zones based on precisely drawn, legally binding lines. Property values, on the other hand, ignore these boundaries, and instead vary based on less tangible factors like proximity to schools, services, and other local amenities. This type of variability is nevertheless real and important in determining the social and ecological character of different locales in or near a city. Boundary models have prevailed in fields such as urban geography, policy, and planning. (B) Gradient models conceptualize cities as nodes or centers of urban-ness, surrounded by differences of many kinds, both social and ecological. Gradient models have been particularly useful in fields such as landscape ecology and urban ecology as a means to explain ecological processes in built environments and the role of cities within larger ecosystems. Both models assume singular, stand-alone urban centers surrounded by relatively undeveloped land, rather than modern urban forms such as pluricentric conurbations or metropolises, even though the latter are becoming common in some parts of the world. The wildland–urban interface (WUI) could be identified at any boundary (A), or anywhere along the urban-to-rural gradient (B), depending on the elements, characteristics, or processes of interest.

Concepts of Peri-Urban Hazards

Many scholars agree that disaster impacts result not solely from external physical shocks, but also from within broader systems.5 In the case of urbanization, for example, threats arise from interactions between cities and their surrounding ecosystems. The emergence of hazards from these interactions generally involves the following: (1) a human community in pursuit of a natural resource or amenity, (2) modification of the biophysical system providing that resource, and (3) a threat that arises as a result of the system modification (Figure 1A). This conceptual model has ushered vulnerability research out of a historically polarized focus on either (a) external biophysical shocks imposed on social systems or (b) inherently social phenomena apart from the biophysical environment.6 Refocusing hazards and vulnerability research from the human or environmental systems themselves toward the interactions between the two has re-invigorated this work within mainstream sustainability science.7

Generalized (A) and specified (B) models for the emergence of environmental hazards from coupled-system interactions. In both models, social systems are coupled with natural systems in multiple ways, across multiple scales, and on multiple time frames. These couplings are thus complex, spatially variable, and dynamic. In the generalized model (A), society encroaches upon nature in pursuit of resources. These could be material (e.g., fuel, food, or fiber), or intangible (e.g., aesthetic amenities like views or solitude). At the same time, society is subject to inescapable ecological processes (e.g., climate, hydrology, nutrient cycling, fire). From these coupled-system interactions, hazards emerge. In the specified model (B), a social/economic system based on residential development encroaches on a natural desert ecosystem. Neighborhoods are developed in pursuit of amenities provided by natural desert surroundings. Housing development, in turn, disturbs desert landscapes to facilitate the invasion of an exotic grass (buffelgrass; Cenchrus ciliaris). Once it becomes dominant on the landscape, buffelgrass enables the spread of wildfire. The stepwise emergence of these two hazards—biological invasion followed by wildfire—threatens both nature (the desert ecosystem) and society (the residential neighborhood). Thus, the residents of this coupled system at the wildland–urban interface find themselves threatened by a hazard as they pursue a suite of natural resource amenities that would not exist if not for these activities.

Figure 1. Generalized (A) and specified (B) models for the emergence of environmental hazards from coupled-system interactions. In both models, social systems are coupled with natural systems in multiple ways, across multiple scales, and on multiple time frames. These couplings are thus complex, spatially variable, and dynamic. In the generalized model (A), society encroaches upon nature in pursuit of resources. These could be material (e.g., fuel, food, or fiber), or intangible (e.g., aesthetic amenities like views or solitude). At the same time, society is subject to inescapable ecological processes (e.g., climate, hydrology, nutrient cycling, fire). From these coupled-system interactions, hazards emerge. In the specified model (B), a social/economic system based on residential development encroaches on a natural desert ecosystem. Neighborhoods are developed in pursuit of amenities provided by natural desert surroundings. Housing development, in turn, disturbs desert landscapes to facilitate the invasion of an exotic grass (buffelgrass; Cenchrus ciliaris). Once it becomes dominant on the landscape, buffelgrass enables the spread of wildfire. The stepwise emergence of these two hazards—biological invasion followed by wildfire—threatens both nature (the desert ecosystem) and society (the residential neighborhood). Thus, the residents of this coupled system at the wildland–urban interface find themselves threatened by a hazard as they pursue a suite of natural resource amenities that would not exist if not for these activities.

Considering urban encroachment on an increasingly dangerous natural environment, it is plausible to think of environmental risk as somewhat socially constructed. Storm surge, for example, threatens no damage to human life or property in places where coastlines remain undeveloped. The physical event occurs, but nothing of value is in its way. In a coastal megacity the same storm surge can be catastrophic. It seems impossible to avoid urbanization in all high-risk environments. How, then, can we limit urban expansion in these areas while also providing much-needed living space? We suggest it is time to accept today's urbanization as a risky endeavor and focus on the circumstances of hazard emergence in and around urban areas. With a keener understanding of these circumstances, we can then consider how to plan and act—both to mitigate hazards before they occur and to adapt afterward. In the storm surge example, significant factors might be the presence of natural wetlands or other protective infrastructure, regulations to promote resilient construction, or the concentration of vulnerable people in relatively safe, or relatively hazardous locales.

Storm surge is one of a multitude of environmental hazards that pose new types and degrees of danger in our current era of rapid urbanization. A better understanding of how hazards emerge where cities interact with changing local ecosystems can help the residents of those cities anticipate and respond to dangerous surprises. Our case study gives insight into pitfalls and opportunities in this pursuit.

Case Study: Tucson, Arizona

We focus on Tucson, Arizona (Figure 2), where rapid suburban real estate development and an exotic grass invasion produce conditions for the unprecedented emergence of wildfire. Located in the southern United States' “sunbelt” region, the city of Tucson is permanent home to ~531,000 and is winter-seasonal home to thousands more. The greater metropolitan population measures more than 1 million. Local topography is defined by isolated mountain ranges surrounded by alluvial slopes called bajadas and separated by extensive, flat basins.8 Biologically diverse Sonoran desertscrub, composed of small trees, shrubs, and succulents, is the predominant vegetation in the basins and bajadas.9 Much of the upland surrounding the city is protected public land managed by federal, state, county, and local agencies.10 Since the early 1900s Tucson has been known as a center for desert exploration, research, and conservation advocacy.11 Today it is a site of innovative, multijurisdictional open space conservation planning.12 The Arizona portion of the Sonoran Desert is contiguous across the international border with that of Sonora, Mexico. Cross-border collaboration on environmental conservation in the Sonoran Desert is a regional tradition.13

The Tucson, Arizona, study site located in the warm, arid region of southwestern North America.

Figure 2. The Tucson, Arizona, study site located in the warm, arid region of southwestern North America.

Tucson's flat basins have been developed for residential, commercial, and industrial land uses over the past two centuries, but the bajadas between the city and surrounding mountains have retained their natural vegetation. In recent decades these areas, known locally as “the foothills,” have been rapidly built up in large subdivisions with homes interspersed throughout the desertscrub (Figure 3). Tucson's peri-urban fringe is a classic example of a wildland–urban interface (WUI), where residential development encroaches on natural areas. Scenic natural features and recreation opportunities are within view or a short drive from anywhere in the city, but property values vary greatly depending on location. Tucson's most expensive homes and its most rapidly growing neighborhoods are located in the foothills WUI zone (Figure 3). As in other sunbelt cities, real estate development is critically important to the local economy. The real estate and construction industries accounted for $5.31 billion in 2013, or 15% of the metropolitan area's gross domestic product.14 A yet untested hypothesis (but a widespread assumption) is that environmental amenities such as scenic vistas, wildlife, and desert solitude play important roles in drawing people to purchase or build homes in Tucson's foothills (J. Betancourt, personal communication). Whether for home-building or recreation, demand on the wildlands surrounding Tucson has never been greater, and it appears that much of that demand depends on these areas remaining wild.

Suburban development at the wildland–urban interface outside Tucson.

Figure 3. Suburban development at the wildland–urban interface outside Tucson. Note: North-facing oblique perspective at top left. Overhead perspective at top right and bottom.

Grass Invasion and Wildfire in the Fireproof Desert

Arguably the greatest ecological threat facing the Sonoran Desert today is buffelgrass (Cenchrus ciliaris), an Indo-African pasture species introduced in the 1940s for erosion control.15 The legacy of buffelgrass throughout the greater desert southwest is longer and complicated, reaching back to the late 1800s and involving aggressive governmental promotion through research, breeding, and commercialization.16 Elsewhere in the region this drought-resistant “wonder grass” was introduced to rehabilitate degraded rangelands.17 Buffelgrass was promoted as a development tool for modernizing the livestock economy in Mexico, where today it is still cultivated on millions of hectares.18 In all its introduction sites, buffelgrass quickly proved itself an aggressive invader—of not only cultivated areas but also disturbed and even undisturbed desert areas.19 Buffelgrass outcompetes native perennial vegetation for water and nutrients and quickly fills in the natural gaps of bare soil between individual shrubs and succulents. This impedes recruitment of long-lived perennials such as giant columnar cactus.20 By the 1990s scientists in Arizona and Mexico had rebranded the wonder grass a “nightmare” for Sonoran Desert ecosystems.21 Today there is abundant rhetoric in the scholarly and popular literature about a “war on buffelgrass.”22

Buffelgrass (Cenchrus ciliaris), an invasive exotic pasture grass and serious fire hazard,surrounds high-end homes in the suburbs of Tucson, Arizona.

Buffelgrass (Cenchrus ciliaris), an invasive exotic pasture grass and serious fire hazard,surrounds high-end homes in the suburbs of Tucson, Arizona.

Desert landscapes are naturally fire resistant because of the wide spacing of individual plants, but buffelgrass covers bare soil with a thick, continuous layer of finely textured, highly flammable fuel that burns at a temperature upward of 870°C.23 Desert plants—particularly succulents—are fire intolerant, so buffelgrass fires are stand-replacing events with permanent impacts. Buffelgrass, by contrast, is a fire-adapted species, so each successive burn destroys competing vegetation and enhances the environmental conditions for its own growth. A grass–fire cycle ensues, in which the formerly fire-resistant desert landscape is converted to a fire-dependent savanna that burns regularly.24 The ultimate ecological problem with buffelgrass invasion, then, is a permanent transformation of the Sonoran Desert vegetation. Unfortunately, climate change will significantly favor buffelgrass, as the relatively warmer winters expected for the region will expand the range of buffelgrass northward and upslope, into locales where the climate was formerly too harsh.25

Buffelgrass (Cenchrus ciliaris) was introduced in the late 19th century to control erosion and later was aggressively engineered as pasturage for widespread introduction to the arid rangelands of southwestern North America.

Buffelgrass (Cenchrus ciliaris) was introduced in the late 19th century to control erosion and later was aggressively engineered as pasturage for widespread introduction to the arid rangelands of southwestern North America.

Wildfire, as an ecological process, is also the mechanism by which buffelgrass presents social problems—most notably the loss of human life, homes, and other property. An editorial in a regional daily newspaper summed up the worry by analogy to suburban wildfires in California:

Everyone understands the terrifying destruction from forest fires and the devastating canyon fires that torch California. We shouldn't wait for whole subdivisions to go up in flames, with the appalling possibility of losing lives, before getting serious about buffelgrass. Time is running short. (The Arizona Republic, 9 April 2010)

The social risks posed by buffelgrass fire are similar to those in other WUI sites where residential development encroaches on fire-adapted ecosystems.26 In Tucson, however, where desert ecosystems evolved in the absence of fire, the hazard is entirely endogenous, generated by dynamics within the system itself. Buffelgrass invasion and fuel buildup are promoted by the very activities (soil disturbance, road building, traffic, etc.) that enable people to inhabit Tucson's desert WUI in the first place. This endogeneity is a key defining feature of emergent environmental hazards in human–environment systems.27

A typical neighborhood in the “foothills” region of the Santa Catalina Mountains north of Tucson, Arizona.

Addressing the Ecological Risk

Tucson's robust scientific community of ecologists and resource managers has waged an aggressive battle against the spread of buffelgrass. Manual and chemical eradication methods have been coupled with equally aggressive public information campaigns (Figure 4). The approach has achieved significant results over the 40 or more years of buffelgrass invasion. In the 1980s buffelgrass made its first appearances in the wildlands around Tucson. It was already present in the city, along roadsides, and in disturbed areas and vacant lots, but the threat was not evident. When buffelgrass turned up in research plots in the federally managed Saguaro National Park and along roadsides, washes, and the steep slopes of Pima County's Tucson Mountain Park, land managers took notice. In Coronado National Forest, the largest swath of federal land bordering Tucson to the north and east, managers watched buffelgrass patches grow and coalesce in the 1990s, and they began to consider ecological risks.

An aggressive public information campaign was launched to raise awareness of the threats posed by buffelgrass and inspire action among Tucson residents. Stylized artwork like this accompanies more informative literature on how to identify the grass and how to remove and dispose of it.

Figure 4. An aggressive public information campaign was launched to raise awareness of the threats posed by buffelgrass and inspire action among Tucson residents. Stylized artwork like this accompanies more informative literature on how to identify the grass and how to remove and dispose of it.

People began to take action. In January 2000 the Arizona-Sonora Desert Museum, Pima County, and Saguaro National Park collaborated to create the Tucson Mountain Weedwackers, a team of volunteers that convened semi-monthly to manually remove buffelgrass from the desert west of the city. Now known as the Sonoran Desert Weedwackers, this grass-roots volunteer group carries on this work today.28 For the past 15 years this group has been led by Pima County Natural Resource Specialist Doug Siegel, whose charisma and passion inspire volunteers new and old. To date the Weedwackers have cleared hundreds of tons of buffelgrass from Tucson Mountain Park. Their efforts, combined with ongoing efforts by Pima County to control larger infestations with herbicide, have maintained the most valued landscapes within Tucson Mountain Park free of buffelgrass to this day.

Another key actor during this period was Julio Betancourt, an interdisciplinary scientist stationed by the U.S. Geological Survey at the Desert Laboratory on Tumamoc Hill in downtown Tucson. When an aging gas pipeline under Tumamoc Hill burst in 2003, Betancourt seized an opportunity to garner environmental impact mitigation funds for buffelgrass control. The effort would serve as a demonstration and outreach project for Pima County. Betancourt hired Travis Bean, a weed ecologist from the University of Arizona, to help him build a public awareness campaign. In 2005 Betancourt and Bean convinced the Arizona Department of Agriculture to declare buffelgrass a noxious weed under Arizona Statute R3-4-244. Shortly thereafter, Pima County adopted Resolution Number 2005-165 stipulating management of buffelgrass and other invasive species.

In 2007 Betancourt, Bean, and leaders from Pima County government, the Arizona-Sonora Desert Museum, and the Pima Association of Governments, the region's federally designated metropolitan planning body, organized a Buffelgrass Summit that was attended by more than 120 representatives from local, state and federal agencies, academia, and private conservation organizations. Summit participants identified a core team and charged it with creating a strategic plan. Within a year the team had completed the plan.

The release of the strategic plan was timed to coincide with a bus tour organized by Betancourt and others to showcase the buffelgrass problem in Tucson's suburbs. Forty government and business leaders took a bus into Tucson's wealthiest neighborhoods in the foothills, where buffelgrass was seen surrounding multi-million-dollar homes. The result was an invitation for Betancourt to present the buffelgrass issue to the Southern Arizona Leadership Council, a group of business leaders that sets economic development priorities for the region. Here Betancourt met Sarah Smallhouse, president of the Thomas R. Brown Foundation and a powerful community leader engaged in a wide range of efforts to improve the economy and quality of life in southern Arizona. She quickly became committed to the fight against buffelgrass. In Smallhouse the movement now had a champion able to gather the necessary financial resources to enact a key recommendation of the strategic plan, to found a nonprofit organization as a regional buffelgrass coordination center. This organization would be the information clearinghouse, volunteer network, and fiduciary agent to receive and distribute funds for high-priority action against buffelgrass throughout the region.

The Southern Arizona Buffelgrass Coordination Center (SABCC) was incorporated as a 501(c)3 nonprofit organization in December 2008. Lindy Brigham, a research scientist at the University of Arizona, was hired as the executive director. In its first 5 years SABCC generated extensive media coverage, sparked congressional field hearings, and facilitated communication across agencies, leading to collaborative efforts to obtain additional funding for buffelgrass treatment. All of these things increased public awareness of buffelgrass as a threat. Most notably, the Federal Emergency Management Agency (FEMA) awarded SABCC and Pima County a $3.4M pre-disaster mitigation grant to reduce the risk of buffelgrass-fueled fires to critical infrastructure within the city.

This grant was in part aimed at protecting low-income neighborhoods from scorching buffelgrass flash fires. Among the critical infrastructure to be protected was the international airport, which had become almost surrounded by buffelgrass in roadsides, dry washes, and empty lots. Ecologically these sites are ideal buffelgrass habitats, and socially these clandestine public spaces are often used by vulnerable people, for example, the homeless and unsupervised children.

Despite the accomplishments set in motion by the FEMA grant, SABCC struggled to find funding to support its own modest operating budget. In 2015, Executive Director Brigham announced plans to retire the following year. This development, coupled with the constant battle to keep SABCC afloat financially, launched the board of directors into a year-long discussion about SABCC's fate. They decided to hand over SABCC's work to more established organizations better positioned to carry it out over the long term. The job of coordinating the regional effort to manage buffelgrass went to the Arizona-Sonora Desert Museum, an organization that had been on the forefront of the buffelgrass movement and had worked closely with SABCC since its founding. Tucson Clean and Beautiful and Sky Islands Alliance, local environmental advocacy organizations focused on the urban environment and wildlands, respectively, took on outreach and pledged to maintain and build new volunteer efforts.

SABCC's biggest accomplishment was facilitating communication among the numerous smaller organizations (federal and local agencies, scientists, grassroots volunteers) that had—some for years—been tirelessly fighting buffelgrass on the ground. Among these groups Saguaro National Park had long been a leader. Biologists, including Danielle Foster and Dana Backer, had been among the first to recognize the threat buffelgrass posed to the park and its namesake giant cactus (Carnegiea gigantea). By 2010 it was apparent that existing tactics (manual removal and on-the-ground treatment with herbicide) were insufficient to deal with the park's 800 hectares of buffelgrass. In 2014 Saguaro National Park collaborated with local, state, and other federal agencies to test aerial application of herbicide via helicopter for remote infestations, which has helped staff limit the extent of the infestation in the park. Saguaro National Park and the National Park Service more generally have shown that scientifically informed control programs, when adequately funded, can be very effective.

Saguaro National Park also applied for and received funding from the Department of Interior's Wildland Fire Resilient Landscapes program (WFRL), which emphasized collaborative landscape-scale planning across multiple jurisdictions to lessen the risk from catastrophic wildfire and enhance the protection of critical natural resources. This effort was led by Backer, who had remained with the park since she began as an intern in the early 2000s. Funding from the WFRL program provided more than half a million dollars to southern Arizona land management agencies to fight buffelgrass during its brief 3-year existence. (The program was eliminated in 2017 with the change in administration at the federal level.) This funding has allowed agencies to extend their work beyond what they could achieve with their annual base funding for invasive species and fire. Another benefit of WFRL money was that it could be easily distributed across jurisdictions. This reliable source of multiyear funding, combined with the ability to distribute these funds to local, state, and federal agencies, universities, and private organizations, brought partners together with renewed enthusiasm. The future of this program, however, is uncertain.

While Saguaro National Park was making headway, Coronado National Forest was losing ground. Staff in a wide variety of positions worked on invasive species problems in piecemeal efforts until 2010, when an ecologist with the Santa Catalina District of Coronado National Forest was enlisted to create a forest-wide invasive species program with a focus on buffelgrass. But by 2010 this district already had an extensive buffelgrass infestation. Staff had been spread thin since the submission in 2007 of a highly controversial proposal for a large open pit mine in the nearby Santa Rita District. Other obstacles included high staff turnover and the loss of resources required to deal with the increasing frequency, severity, and size of wildfires in Forest Service lands throughout the state. Current estimates of the extent of buffelgrass in the Santa Catalina District are 4,000–5,000 hectares. The discontinuation of the WFRL program may result in rapid expansion of buffelgrass in the coming years.

Addressing the Human Risk

While scientists and resource managers have battled buffelgrass as a threat to desert ecosystems, buffelgrass has become a prominent subject of fire safety planning at state and local levels. All local Tucson agencies, including municipal fire departments, are well aware of the risks posed by buffelgrass. In Pima County's 2013 Draft Community Wildfire Protection Plan, buffelgrass figures prominently as a fuel source in need of control. Local communities that demonstrate precautionary measures against wildfire are recognized through the National Fire Protection Association's Firewise USA program (http://www.firewise.org/about.aspx). Following recommendations of the Arizona Department of Forestry and Fire Management, residents of Pima County are instructed to remove fuels like buffelgrass and reduce the height and volume of remaining vegetation. They are instructed also to create space between plants, structures, and other plants. Following these guidelines, a buffelgrass-infested property could be returned to the widely spaced open canopy typical of natural desert vegetation.

In light of these guidelines and recommendations, we might ask what residents are actually doing to protect themselves against wildfire. In 2010 a random selection of 122 Tucson homeowners responded to a survey about buffelgrass and its associated risks. Ninety percent reported some degree of awareness that buffelgrass poses a threat to the Sonoran Desert. Buffelgrass invasion and residential development were each considered the primary threat by 44% of respondents. Many respondents reported both these threats as primary, and some acknowledged a link between the two. When presented a list of more specific concerns about buffelgrass, 34% cited that it fuels wildfires, followed by 18% indicating that invasion will be uncontrollable, and 9% indicating that buffelgrass will outcompete native plants. These widely recognized threats are among those most commonly identified in the public information campaigns organized by Bean and Betancourt. Respondents here thus echo the concerns of the local scientific community.

Buffelgrass, a fire-adapted species, quickly fills in the spaces between desert plants, forming a continuous layer of highly flammable fuel. This photo shows a post-fire landscape.

Buffelgrass, a fire-adapted species, quickly fills in the spaces between desert plants, forming a continuous layer of highly flammable fuel. This photo shows a post-fire landscape.

More interesting, perhaps, are the threats not anticipated by residents. More than 93% had nothing to say about damage to homes, depreciation of property values, adverse impacts on real-estate markets, degradation of views, damage to publicly funded protected areas, or other burdens on public financial and human resources.

There was remarkably little recognition of residents' own lives and property at risk. This became apparent in a mapping exercise, in which residents were asked to indicate locales in and around Tucson most threatened by buffelgrass invasion. Overwhelmingly, residents pointed to wildlands outside the city, not to places where they live and work. Thus, while homeowners seem to be aware that buffelgrass promotes wildfire, and they recognize that buffelgrass therefore threatens desert ecosystems, they are largely unaware that buffelgrass could affect them or their property. Buffelgrass and wildfire threats are perceived as an ecological problem out there in the desert, apart from people's day-to-day activities. This finding is troubling in light of a decade of research calling attention to urban centers and WUI areas as sites of buffelgrass invasion, and more recent concerns among municipal officials about the danger of buffelgrass fires in central city locations (J. Betancourt, personal communication).

Buffelgrass quickly colonizes open land, especially areas of soil disturbance by water or foot traffic. Urban washes, often close to homes, are particularly vulnerable.

Buffelgrass quickly colonizes open land, especially areas of soil disturbance by water or foot traffic. Urban washes, often close to homes, are particularly vulnerable.

What about homeowners' perception of the hazard as it emerges? Photographs in the survey measured respondents' ability to identify various stages of buffelgrass invasion on desert landscapes. The results showed limitations in homeowners' ability to see buffelgrass when interspersed among other desert plants. Although 84% could correctly locate buffelgrass in a fully invaded landscape, 49% could identify no buffelgrass at all when it occurred as dispersed individuals or small to mid-sized patches. This perceptual shortfall is critical because the difference between incipient and advanced invasion is a matter of several tons of fuel per hectare. Furthermore, interventions such as pulling or spraying are most effective in the early stages of invasion, and much less so in advanced stages. The inability of respondents to see buffelgrass is ironic in light of their stated preferences for action. When asked what should be done about buffelgrass, 72% called for “eradication” or “control” rather than “management,” yet about half the respondents could not identify buffelgrass until the invasion before their eyes had advanced too far for either eradication or control. Experts think that region-wide eradication and control of buffelgrass are no longer possible (J. Betancourt, personal communication). The agencies involved have thus adopted a strategy of local eradication in top-priority sites, larger-scale but less intensive control in areas of high conservation value, and management and restoration across the region.29

A survey is underway to ascertain to what degree Tucson residents are following recommendations set forth in the Community Wildfire Protection Plan and the Firewise USA program. Until those results are in, we cannot know how well prepared homeowners are for the hazards facing them and their property.

Conclusion: Lessons Learned and Applied

To conclude this story, we discuss the successes and shortcomings in Tucson's response to buffelgrass and wildfire in ecological as well as human terms. Invasive plants and wildfire are environmental hazards that many communities throughout the world must learn to live with in the Anthropocene era.30 We believe lessons from the Tucson case have broad relevance to the understanding and mitigation of urban hazards wherever they might emerge. Further, some lessons could be applied to any urban area, regardless of hazard type.

Tucson's remarkable success against the spread of buffelgrass owes in large part to the passion of individuals who recognized an impending ecological disaster early on and took action, despite the enormity of the problem and a high probability of failure. Tucson was fortunate to have many such people who played complementary roles. Betancourt was critical for engaging key government figures at the federal, state, and local levels, as well as business leaders. Backer was relentless in fighting buffelgrass on the ground, and her efforts paid off in Saguaro National Park. She also led the effort to secure WFRL funds that nearly doubled the area of buffelgrass in the Tucson Basin under annual treatment. Siegel demonstrated the power of an enthusiastic and charismatic leader to do significant work with volunteers and minimal financial resources. The involvement of Smallhouse and the Southern Arizona Leadership Council represented a critical bridge between the science and business communities. The bus tour of Tucson's million-dollar homes at risk helped community leaders see an ecological problem as a socioeconomic problem. The success of SABCC owed in large part to its independence as a nongovernmental organization. Even though operations funding was insecure, SABCC was nevertheless able to wield significant social capital and become a cross-jurisdictional collaboration broker.

The Tucson story follows many other case studies in demonstrating how grass-roots volunteer work can make significant headway toward the solution of environmental problems. Grass-roots initiatives are by definition collaborative, but they are initiated by charismatic leaders and catalyzed by a sense of camaraderie and community. It is remarkable, then, that environmental volunteerism has been so effective in a place known for recent immigration and seasonal residency. The surprisingly strong sense of place attachment and the common appreciation of the Sonoran Desert ecosystem among volunteers are testaments to the work of organizations like the Arizona-Sonora Desert Museum and Saguaro National Park.

Although the public seems to be rallied around saving the Sonoran Desert from buffelgrass invasion, there is no such groundswell of action to save neighborhoods from buffelgrass fires. The most striking result of our case study may be the disparity in public awareness of ecological and human threats. This is ironic given that the scientific community uses public safety as its main argument for environmental protection. Support for the war on buffelgrass is usually justified by outlining the threats posed to human life and property. Scientists appeal to residents to save their homes, while residents step up and volunteer to save the desert. This situation reveals a persistent gap at the interface between science and practice in the environmental hazards field.31 In the Tucson case, the fact that volunteerism to remove buffelgrass from desert landscapes also mitigates the risk of home losses seems to be little more than a fortunate coincidence.

Sometimes motivation surrounding things the public cares about can spill over to support other things the public is unaware of or unmotivated to act on. For example, highlighting the threat of wildfire to people's homes has been relatively ineffective at motivating concern about buffelgrass, but highlighting the potential loss of the iconic saguaro cactus from the Sonoran Desert landscape has been highly effective (T. Bean, personal communication).

 patchy carpet of invasive exotic buffelgrass (Cenchrus ciliaris) encroaches upon Tucson International Airport.

A patchy carpet of invasive exotic buffelgrass (Cenchrus ciliaris) encroaches upon Tucson International Airport.

In several ways, the emergence of wildfire in and around Tucson has relevance to the issues other cities face as they rapidly grow. All cities, for example, are composed of a mix of long-term residents and newcomers. The lands they rest on are governed as a multijurisdictional patchwork by multiple agencies. The environments that surround cities are in some ways dangerous. Finally, the human–environment interactions by which those cities grow, such as residential development, agriculture, or forestry, put dynamic pressures on local environments. All of these conditions make for a precarious situation in an era of environmental change, and they increase the likelihood of hazard emergence. The Tucson case shows how cities can enhance their resilience in the face of these realities by creating pathways for collaboration, supporting the work of key individuals, and cultivating a sense of place among residents.

Tucson's buffelgrass infestations worsen in the areas where they have been ignored. However, infestations have been remarkably reduced or even eliminated in areas that have been adopted as priority sites by agency personnel and volunteers. How much buffelgrass exists across the Tucson Basin is almost impossible to know, so a current assessment of the risk remains difficult. The fundamental problem of not knowing how much buffelgrass is out there or where it is makes the success of volunteer efforts even more remarkable. The combination of a strong sense of place among Tucson residents and the dedicated, well-coordinated efforts to educate the public about buffelgrass has thus far been an effective means of controlling the invasion in the places that the people of Tucson care about most.

NOTES

1. J. Hansen et al., “Assessing ‘Dangerous Climate Change': Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature,” PLoS ONE 8, no. 12 (December 3, 2013): e81648, doi:10.1371/journal.pone.0081648.

2. W. Solecki, M. Pelling, and M. Garschagen, “Transitions between Risk Management Regimes in Cities,” Ecology and Society 22, no. 2 (2017), doi:10.5751/ES-09102-220238.

3. Ibid.

4. C. S. Holling, “The Resilience of Terrestrial Ecosystems: Local Surprise and Global Change,” in W. C. Clark and R. E. Munn, eds., Sustainable Development of the Biosphere (Cambridge, UK: Cambridge University Press, 1986), 292–316.

5. P. Blaikie, T. Cannon, I. Davis, and B. Wisner, At Risk: Natural Hazards, People's Vulnerability and Disasters, 2nd ed. (London, UK and New York, NY: Routledge, Taylor & Francis Group, 2004).

6. P. Robbins, J. Hintz, and S. A. Moore, Environment and Society: A Critical Introduction, 2nd ed. (Malden, MA: Wiley-Blackwell, 2014).

7. B. L. Turner et al., “A Framework for Vulnerability Analysis in Sustainability Science,” Proceedings of the National Academy of Sciences 100, no. 14 (2003): 8074–79.

8. R. Scarborough, “The Geologic Origin of the Sonoran Desert,” in A Natural History of the Sonoran Desert (Tucson, AZ, and Berkeley, CA: Arizona-Sonora Desert Museum Press and University of Carlifornia Press, 2000), 71–86.

9. M. A. Dimmit, “Biomes and Communities of the Sonoran Desert,” in A Natural History of the Sonoran Desert (Tucson, AZ, and Berkeley, CA: Arizona-Sonora Desert Museum Press and University of California Press, 2000), 3–18.

10. R. M. Marshall et al., “An Ecological Analysis of Conservation Priorities in the Sonoran Desert Ecoregion” (Tucson, AZ, and Hermosillo, Sonora, Mexico: The Nature Conservancy Arizona Chapter, Sonoran Institute, and Instituto del Medio Ambiente y el Desarrollo Sustentable del Estado de Sonora [Environment and Sustainable Development Institute of the State of Sonora], with support from Department of Defense Legacy Program, Agency and Institutional partners, 2000).

11. W. G. McGinnies, Discovering the Desert: Legacy of the Carnegie Desert Botanical Library (Tucson, AZ: University of Arizona Press, 1981).

12. Pima County Government, “Sonoran Desert Conservation Plan: A Long Term Vision for Protecting the Heritage and Natural Resources of the West,” 2006, http://www.pima.gov/CMO/SDCP.

13. W. Laird-Benner and H. Ingram, “Surprising Environmental Successes on the U.S./Mexico Border,” Environment 53, no. 1 (2011): 6–16.

14. Bureau of Economic Analysis (BEA), “Regional Economic Accounts,” 2015.

15. J. M. Stevens and D. A. Falk, “Can Buffelgrass Invasions Be Controlled in the American Southwest? Using Invasion Ecology Theory to Understand Buffelgrass Success and Develop Comprehensive Restoration and Management,” Ecological Restoration 27, no. 4 (2009): 417–27.

16. J. C. Brenner, “Pasture Conversion, Private Ranchers, and the Invasive Exotic Buffelgrass (Pennisetum ciliare) in Mexico's Sonoran Desert,” Annals of the Association of American Geographers 101, no. 1 (2011): 84–106.

17. E. C. Bashaw, “Buffelgrass Origins,” in “Buffelgrass: Adaptation, Management, and Forage Quality” conference (Texas A&M University Research and Extension Center, Weslaco, TX, 1984), 6–8.

18. K. A. Franklin et al., “Buffelgrass (Pennisetum ciliare) Land Conversion and Productivity in the Plains of Sonora, Mexico,” Biological Conservation 127 (2006): 62–71.

19. J. C. Brenner and L. L. Kanda, “Buffelgrass (Pennisetum ciliare) Invades Lands Surrounding Cultivated Pastures in Sonora, Mexico,” Invasive Plant Science and Management 6, no. 1 (March 2013): 187–95, doi:10.1614/IPSM-D-12-00047.1.

20. A. D. Olsson et al., “Sonoran Desert Ecosystem Transformation by a C4 Grass Without the Grass/Fire Cycle,” Diversity and Distributions 18, no. 1 (2012): 10–21, doi:10.1111/j.1472-4642.2011.00825.x.

21. D. Yetman and A. Búrquez, “Buffelgrass—Sonoran Desert Nightmare,” Arizona Riparian Council News 7, no. 1 (1994): 8–10.

22. B. W. Poole, “Help Wanted in War Against Buffelgrass,” Tucson Citizen, November 26, 2007, sec. Local.

23. C. J. McDonald and G. R. McPherson, “Fire Behavior Characteristics of Buffelgrass-Fueled Fires and Native Plant Community Composition in Invaded Patches,” Journal of Arid Environments 75, no. 11 (November 2011): 1147–54, doi:10.1016/j.jaridenv.2011.04.024.

24. A. Búrquez-Montijo, M. E. Miller, and A. Martínez-Yrizar, “Mexican Grasslands, Thornscrub, and the Tranformation of the Sonoran Desert by Invasive Exotic Buffelgrass (Pennisetum Ciliare),” in Invasive Exotic Species of the Sonoran Region (Tucson, AZ: University of Arizona Press and Arizona-Sonora Desert Museum, 2002), 126–46.

25. J. L. Weiss and J. T. Overpeck, “Is the Sonoran Desert Losing Its Cool?,” Global Change Biology 11 (2005): 2065–77.

26. D. E. Calkin et al., “How Risk Management Can Prevent Future Wildfire Disasters in the Wildland-Urban Interface,” Proceedings of the National Academy of Sciences 111, no. 2 (January 14, 2014): 746–51, doi:10.1073/pnas.1315088111.

27. B. L. Turner et al., note 7; B. L. Turner et al.,“Illustrating the Coupled Human–Environment System for Vulnerability Analysis: Three Case Studies,” Proceedings of the National Academy of Sciences 100, no. 14 (2003): 8080–85.

28. M. Hanson et al., “Sonoran Desert Weedwackers: A Model for Controlling the Spread of Invasive Grasses,” in Invasive Plants on the Move: Controlling Them in North America (Tucson, AZ: Arizona-Sonora Desert Museum Press, 2009).

29. Stevens and Falk, note 15.

30. M. A. Moritz et al., “Learning to Coexist with Wildfire,” Nature 515, no. 7525 (November 6, 2014): 58–66, doi:10.1038/nature13946; L. Head et al., “Living with Invasive Plants in the Anthropocene: The Importance of Understanding Practice and Experience,” Conservation & Society 13, no. 3 (2015): 311–18.

31. C. Vogel et al., “Linking Vulnerability, Adaptation, and Resilience Science to Practice: Pathways, Players, and Partnerships,” Global Environmental Change 17, no. 3–4 (2007): 349–64.

The authors gratefully acknowledge the support, assistance, and insight of many others who do not appear in the byline. Samuel Walker conducted the survey of Tucson residents in 2010. Julio Betancourt provided guidance on the preparation of the article and reviewed preliminary drafts. Lindy Brigham, Travis Bean, Neal Kittelson, Dana Backer, Marilyn Hanson, Sharon Biedenbender, Michele Girard, and Doug Siegel provided comments that refined and improved the case-study narrative.

 

Jacob C. Brenner is an associate professor of environmental studies and sciences at Ithaca College in upstate New York. He has worked on and off in the Sonoran Desert of Arizona and Sonora, Mexico, since 2000. During 2007–2010 he worked intensively with Sonoran ranchers to better understand the reasons why they cultivate bufffelgrass, along with the social and ecological implications of those decisions.

Kimberly A. Franklin is a conservation research scientist with the Arizona-Sonora Desert Museum, a highly esteemed nonprofit organization based in Tucson, Arizona, that helped launch the original grass-roots campaign to stop the spread of buffelgrass in the Tucson Basin. She has worked on both biological and social aspects of the buffelgrass invasion in the Sonoran Desert since 2005.

 

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